Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), resistive memory (e.g., RRAM), and Flash memory, among others.
Memory devices are utilized as volatile and non-volatile data storage for a wide range of electronic applications. Flash memory, which is just one type of memory, typically uses a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), digital cameras, cellular telephones, portable music players such as MP3 players, movie players, and other electronic devices. Memory cells can be arranged into arrays, with the arrays being used in memory devices.
A memory cell of a memory device can be programmed to a desired data state. For example, a single level cell (SLC) can be programmed to one of two data states, such as a logic high or binary “1” data state and a logic low or binary “0”data state. Multilevel cells (MLCs) can be programmed to one of more than two data states. For example, some Flash MLC memory cells can be programmed to one of four, eight, or sixteen data states (e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110), where each of these data states is represented by a respective quantity of electric charge placed on or removed from a charge storage structure (e.g., a floating gate). A memory cell can have one or more nodes as part of the structure. As such, MLCs can allow the manufacture of higher density memories without increasing the number of memory cells since each cell can be programmed to one of two data states, and thus, store more than one bit. For these MLCs, the lowermost data state is typically not programmed above the erased state, that is, if the cell is programmed to the lowermost data state, it remains in the erased state rather than, for example, having a charge stored in the cell during a programming operation. The other fifteen data states can be referred to as “non-erased” states.
Some memory cells have wear relative to the quantity of program and erase cycles to which they are subjected. That is, memory cell performance can degrade with repeated use. The extent to which Flash MLCs degrade can also be relative to the amount of charge stored when programmed. That is, data states represented by the storage of relatively larger charge amounts tend to wear a memory cell relatively faster than those data states represented by the storage of relatively smaller charge amounts.